Even after the most brutal losses, when Kevin Garnett visibly seethes, Rajon Rondo's answers to questions are terser than usual and the bad taste of defeat seems to make Paul Pierce want to spit, Doc Rivers is typically measured in his words.

The Celtics coach had a reputation as a fearsome competitor as an All-Star point guard, and as a coach he is no different. But on most nights he invariably lauds the effort of his players, occasionally to a fault, no matter the outcome of the game.

Thursday was not one of those nights.

Rivers was incensed at what he saw as shoddy effort by the Celtics in their 93-86 loss to Chicago. The Celtics lost to the Bulls for the third time this season and fell to one game ahead of the Sixers in the Atlantic Division standings, but above all they played too "cool," according to their coach.

"I had to use two timeouts just to remind us we had an NBA game [Thursday] and that we needed to play hard," Rivers told the media after the game. "I thought this was the worst loss for us this year with the way we approached the game.

"Then in the second half, I thought Chicago, they were just too tough for us. I just thought their toughness made us let go of the rope. You could see it. We wanted to use all the excuses. I just thought Chicago was too tough for us."

Rivers used the same "let go of the rope" phrase his former associate coach and current Bulls head coach Tom Thibodeau used to describe his team's two-game losing streak. The Bulls had kept humming atop the Eastern Conference standings even though their engine, point guard Derrick Rose, was missing his 12th straight game with a sore groin.

Chicago's success the last two seasons has been built on defense, not the exploits of one transcendent point guard, and the Celtics learned that the hard way on Thursday.

"We were 'cool,'" Rivers said. "We were the 'cool' Boston Celtics [on Thursday]. That's what we looked like, walking around, walking the ball up, couldn't get the ball inbounds. Nobody wanted to work to get the ball. It was a joke. You don't play basketball cool."

The Celtics may have played "cool," but that did not help the Bulls hit a shot in the first half. Before halftime they shot 34 percent from the floor, committed eight turnovers and let the Celtics play even in rebounding at 20 boards apiece, even though the Bulls are the top rebounding team in the NBA and the Celtics are the worst.

The third quarter was where things turned disastrous for the Celtics. They were outscored 29-17 in the frame and committed five turnovers.

"I just think we didn't match their energy level in the second half," said Pierce, who admitted he was frustrated by the loss but declined to agree that the Celtics' approach was their worst of the season. "They came out with more purpose. We didn't show the sense of urgency."

Rivers' words were more direct, and he didn't avoid his own wrath.

"That's on me first," Rivers said. "I didn't see something tonight. It's always on the coach. That's not an acceptable effort for us. I don't say that very often. I don't think I've ever said that. That was a crime."